1. Field of the Invention
This invention relates to a disc cartridge where a disc-like recording medium is housed in a cartridge main body constructed of an upper shell and a lower shell.
2. Description of the Related Art
As one example of this type of disc cartridge, Japanese Laid-Open Patent Publication No. 2002-50147 discloses a disc cartridge in which an optical disc is housed in a cartridge case composed of an upper shell, a middle shell, and a lower shell. In this case, the middle shell is formed with a disc-like overall shape and an operated part, which is composed of a gear or the like that can be engaged by a shutter opening/closing means of a recording/reproducing apparatus, is formed in a circumferential surface thereof (a ring part). The middle shell is housed so as to be able to rotate within the casing formed by the upper shell and the lower shell. Openings that enable the recording and reproduction of recording data (i.e., disc access) for an optical disc in a housed state are formed in the middle shell and lower shell, with these openings being opened and closed by a pair of shutter members. In this case, the shutter members are formed with overall plate-like shapes and are formed with shaft parts, which are inserted through a support hole of the middle shell, and opening/closing channels into which operating projecting parts of the lower shell are inserted so as to pass through. By rotating the middle shell with respect to the lower shell, the shutter members are caused to slide by the middle shell to open and close the openings in the lower shell and the middle shell.
With this disc cartridge, in a normal state the opening in the lower shell is closed by the pair of shutter members and the middle shell. When the disc cartridge has been loaded into a recording/reproduction apparatus, the middle shell is rotated by the shutter opening/closing means of the recording/reproducing apparatus. At this time, the opening in the lower shell and the opening in the middle shell overlap in the thickness direction and the shutter members are caused to slide as the middle shell rotates so as to move away from each another. As a result, the opening in the lower shell is opened and disc access for the optical disc inside the disc cartridge becomes possible. On the other hand, when the disc cartridge is ejected from the recording/reproduction apparatus, the middle shell is rotated in the opposite direction to during loading by the shutter opening/closing means of the recording/reproducing apparatus. At this time, the openings in the lower shell and the middle shell cease to overlap, and the shutter members are caused to slide so as to move closer to each other as the middle shell rotates, thereby closing the opening. By doing so, the opening is opened or closed according to whether disc access is required for the optical disc.
However, by investigating the above conventional disc cartridge, the present inventors discovered the following problem. That is, with the above disc cartridge, the opening is opened or closed by the shutter opening/closing means of the recording/reproducing apparatus rotating the middle shell of the above disc cartridge so that the middle shell causes the pair of shutter members to slide with respect to the lower shell. In this case, when the middle shell is being rotated, the shaft parts of both shutter members are rotated in the support hole of the middle shell and the operating projecting parts of the lower shell are caused to relatively slide within the opening/closing channels of both shutter members. Accordingly, when opening and closing both shutter members, a large amount of force is required to rotate the middle shell (i.e., to open and close the shutter members) due to factors such as the sliding resistance between an edge of the support hole in the middle shell and circumferential surfaces of the shaft parts of the shutter members and the sliding resistance between edges of the opening/closing channels of the shutter members and the operating projecting parts of the lower shell. This means that with a conventional disc cartridge, there is the problem that it is difficult to smoothly open and close the shutter members. Since two shutter members are provided inside the cartridge casing, the conventional disc cartridge also has a problem in that the assembly process for the disc cartridge is complex, resulting in a high manufacturing cost.